Deletion of the C-terminal ESEV domain of NS1 does not affect the replication of a low-pathogenic avian influenza virus H7N1 in ducks and chickens

International audienceHighly pathogenic avian influenza (HPAI) H7N1 viruses caused a series of epizootics in Italy between 1999 and 2001. The emergence of these HPAI viruses coincided with the deletion of the six amino acids R225VESEV230 at the C-terminus of NS1. In order to assess how the truncation of NS1 affected virus replication, we generated by reverse genetics a wild-type low pathogenic avian influenza (LPAI) H7N1 virus with a 230 amino acid long NS1 (H7N1230) and a mutant virus with a truncated NS1 (H7N1224). The six amino acids truncation had no impact on virus replication in duck or chicken cells in vitro. The H7N1224 virus and the H7N1230 virus also replicated to similar levels and induced similar immune responses in ducks or chickens. No significant histological lesion was detected in infected ducks regardless of the virus inoculated. However, in chickens, the H7N1230 induced a more severe interstitial pneumonia than the H7N1224 virus. These findings indicate that the C-terminal extremity of NS1, including the PDZ-binding motif ESEV, is dispensable for efficient replication of a LPAI virus in ducks and chickens, even though it may increase virulence in chickens, as revealed by the intensity of the histological lesions